The present invention relates to a shield case for housing an electronic circuit-mounting printed circuit board by utilizing double shield noise reduction.
Electronic circuits such as controllers are surface-mounted on a printed circuit board, and the printed circuit board is housed in a case. The case is connected to a control board or grounded to protect and insulate the electronic circuits from electrostatic noise, electromagnetic interference (EMI) and power source noise. Signal ground terminals of the electronic circuits are connected to a common ground terminal in the case.
In order to improve anti-noise characteristics, conventional cases employ a double shield structure. The case has a metal plate for guaranteeing mechanical strength and a shield plate mounted on the metal plate to achieve double insulation. Therefore, the structure is complicated, and assembly is cumbersome. When an inexpensive iron series material is used to constitute the metal plate, the potential gradient often becomes large due to electrostatic noise. Hence, a good double shield effect cannot be provided.